In recent years, the substantial increases in costs of basic materials such as plastics, cement, asphalt and the like has encouraged development and use of filler materials to reduce the amount and cost of the basic materials used and the weight of the finished materials. One of the newly suggested filler materials utilizes hollow glass or plastic microspheres. The known methods for producing hollow glass or plastic microspheres for use as filler materials, however, have not been successful in producing microspheres of uniform size or uniform thin walls which makes it very difficult to produce filler and insulation materials of controlled and predictable physical and chemical characteristics and quality.
In recent years, the substantial increases in the energy costs of heating and cooling has also encouraged the development of new and better insulation materials and many new insulation materials have been developed in an attempt to satisfy this need.
The known methods for producing hollow glass, plastic or metal microspheres, other than the L. B. Torobin patents discussed below, have not been successful in producing microspheres of relatively uniform size or uniform thin walls which made it very difficult to produce materials of controlled and predictable characteristics and quality.
One of the existing methods of producing hollow glass microspheres, for example, as disclosed in the Veatch, et. al. U.S. Pat. No. 2,797,201 or Beck, et. al. U.S. Pat. No. 3,365,315 involves dispersing a liquid and/or solid gas-phase precursor material in the glass material to be blown to form the microspheres. The glass material containing the solid or liquid gas-phase precursor enclosed therein is then heated to convert the solid and/or liquid gas-phase precursor material into a gas and is further heated to expand the gas and produce the hollow glass microspheres containing therein the expanded gas. This process is, understandably, difficult to control and of necessity, i.e. inherently, produces glass microspheres of random size and wall thickness, microspheres with walls that have sections or portions of the walls that are relatively thin, walls that have holes, small trapped bubbles, trapped or dissolved gases, any one or more of which will result in a substantial weakening of the microspheres, and a substantial number or proportion of microspheres which are not suitable for use and must be scrapped or recycled.
Neither the Veatch, et. al. U.S. Pat. No. 2,797,201 nor Beck, et. al. U.S. Pat. No. 3,365,315 disclose adding fibers to the glass microspheres to reinforce and strengthen the microspheres.
Though there have been recently described methods of producing uniform size hollow glass microspheres (Torobin U.S. Pat. No. 4,303,431), uniform size hollow metal microspheres (Torobin U.S. Pat. No. 4,415,512) and uniform size plastic microspheres (Torobin U.S. Pat. No. 4,303,603), there has been no teaching of adding fibers to the glass, metal or plastic materials to make fiber reinforced hollow microspheres and/or to improve the tensile strength of the microspheres.
The known methods for producing hollow glass, metal or plastic microspheres have not been used to make fiber reinforced hollow microspheres.